Electric heater



Ap 1939- c. P. RANDOLPH ELECTRIC I HEATER Filed May 15, 1936 Inventor:Chow-\es F? F? ndol'ph, y WMZ ILJML is Attorneu.

Patented Apr. 18, 1939 UNITED STATES 2,155,239 ELECTRIC HEATER 7 CharlesP. Randolph, Oak Park, 111., assignor to Edison General ElectricAppliance Company, Incorporated, Chicago, 111., a corporation of NewYork Application May :15, 193 Serial ,No. 79,887 1 Claim. (01. 201-6 1)This invention relatesto electric heaters, more particularly to electricheaters of the metallically sheathed type, and it has forits object theprovision of an improved terminal structure for heaters of thischaracter which is electrically and mechanically strong and which isimpervious to moisture and dirt. n 7

Although this invention has other applications, it is particularlyuseful in connection with electric immersion heaters of the type havingan encased or sheathed heating unit in which an insulated resistanceconductor is enclosed in; an outer metallic protective casing. Oneimmersion heater of this type is described and claimed in the UnitedStates Patent to C. C. Abbott, No. 1,322,992, dated January 13, 1925. 1

.As there described, the heater is formed into the shape of a hair pinso thatits terminal ends are adjacent each other. ,Some difllculty hasbeen experienced with heaters of this type due to electrical break-downof the terminals during severe electrical storms, such as occur, forexample, in thesouthern states of the United States. 1 g

It is an object-of thisinvention to increase materially the electricalstrength of the terminals of electrical heaters, especially those ,ofthe immersion type referred to above. ,At' the same time, this inventioncontemplates a mechanically strong terminal construction, and one thatis moisture and dirt proof.

In accordance with this invention, the ends of the sheath and theterminals projecting therefrom are embedded in a substantiallyhomogeneous mass of electrically insulating and sealing material. It iscontemplated that this mass of material have a high electricalresistance and also a relatively great mechanical strength.

For a more complete understanding of this invention, reference should behad to the accompanying drawing in which Fig. 1 is a fragmentaryelevation of an electric heater embodying this invention, portions beingbroken away and portions shown in section so as to illustrate certaindetails of construction; and Fig. 2 is an end elevation of the electricheater of Fig. 1.

Referring to the drawing, I have shown my invention in one form inconnection with an electric immersion heater of the type described andclaimed in the above-mentioned Abbott patent. This heater is providedwith a pair of sheathed heating units Ill mounted in a suitablesupporting member II. The heating units Ill have substantially the sameconstruction, and each heater, as shown, is of the helical coil sheathedtype,

, ly insulating disc-shaped mass of sealing material described andclaimed in the United States Patent to C. C. Abbott No. 1,367,341, datedFebruary 1, 1921. Briefly, eachheater comprises an outer metallic sheathI2 in which a helical, electrical resistance conductor i3 isembedded'ina com- I pacted mass of powdered heat refractory,electrically insulating material it, such as magnesium oxide. ,Theresistance conductor I3 has its ends secured in any suitable manner toelectrical terminals I5 which project from'the ends of the sheath andwhich have theirinner ends, as shown, embedded in the insulating mass M.Such units can be bent easily into any desired shape. In the immersionheater shown, each heating unit is bent substantially in the form 15 ofa hairpin. Clearly, various other arrangements and configurations of theheating unit may be used.

The ends of each hairpin heating unit ID, as shown, are directed throughsuitable spaced apertures l6 provided for them in the metallicsupporting member it so to pass through irom one side to the other ofthe supporting 18. This mass of material i8 preferably will be formed ofa suitable phenol condensation product.

Preferably, the bushings il will be so proportioned that their outerfaces will not extend to the outer face of the support i l, but willfall short thereof so as to provide shallow recesses 19. These recesseswill be filled with the insulating sealing material I8. These recessesassist in anchoring the insulating mass.

Also, it is preferable that the mass of powdered insulating material 14in the sheath come substantially close to the ends of the sheath, butnot quite to these ends, so that relatively shallow cup-shaped recesses20 are provided in the ends. These recesses also are filled with theinsulating sealing material so that the ex- Hosed portions of theinsulating material 14 at the sheath ends are completely covered by therial I4, and thereby increases the electrical strength of the heater.

Secured to the outer ends of the terminals ll are terminal connectionmembers 2l= shown to be in the form of nuts threaded to the terminals.The lower ends of these members 2|, as shown, are knurled and theseknurled portions are'embedded in the insulating mass ll so as to securethe members 2| rigidly to the terminals, and so as to insulate them fromeach other.

In making the electric heater thus far described, it will be understoodthabthe heating units l0 will be constructed in the form of hairpins,and their ends will be projected through the apertures It provided forthem in the support II and secured to the support by means oi thebushings ll. Previous to this the ends of the sheath will be reamed outto provide the recesses 2!. Then the terminal members 2| will bethreaded on the terminals. After this, the mass of insulating materialI8 will be applied. This insulating material may be applied in anysuitable fashion, but preferably will be applied autosmall nuts 25secure the jumpers to the opposite pair of terminals.

It will be observed that the mass of insulating and sealing material l8projects for a material distance from the metallic plate II. Thus, itforms a sealing mass embedding the ends of the sheath and the terminalsto remove the terminals electrically from the sheath l2 and thesupporting plate I I, as well as from each other.

Moreover, it will be observed that the insulating mass 18 covering theexposed ends of the insulating material i4, and embedding the ends ofthe sheath and the terminal portions which project from the sheathcompletely seals the heating unit against the admission of moisture anddirt.

It is also to be noted that the insulating mass [8 is anchored solely bythe support II, the projecting ends of the sheath, the terminals andterminal connector members 2|, the adherence of the insulating mass tothese members constituing the sole supporting means for the mass.

The connector members 2| are rigidly sec by the insulating mass. Thisarrangement with the rigid structure eiiected by the Jumpers at theterminal ends makes a very strong terminal structure.

Ithasbeeniound thatmyterminalsealis superior mechanically and alsoelectrically to those in-use heretofore. The electrical superiority isparticularly noticeable in those sections of the country where severeelectrical storms occur. Previous to this invention, diiiiculty wasexperienced by electrical break-down oi the terminals. This inventionhas obviated this diiiiculty.

While I have shown a particular embodiment of my invention, it will beunderstood, 0! course, that I do not wish to belimited thereto sincemany modifications may be made, and I, therefore, contemplate by theappended claim to cover any such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent 0! the UnitedStates, is:

An electric heater comprising a resistance conductor, a metallic sheathencasing said conductor having its ends adjacent each other, terminalswithin the end portions of said sheath connected with said resistanceconductor and projecting from said ends, a mass of ctrically-insulating,heat-conducting material bedding said resistance conductor and the innerends of said terminals, said mass extending not quite to the ends orsaid sheath so as to leave shallow cup-shaped recesses in said ends, ametallic support having spaced apertures extending through it throughwhich the ends of said sheath are passed from one side to the other ofsaid support so as to project beyond the latter side of said support, asingle, substantially homogeneous disc-like mass of electricallyulatiggsealing material molded on said side a d projfiting therefrom to embedthe projecting ends of said sheath and the terminals projecting fromsaid ends and so as to fill said recesses in said sheath, and terminalmembers having exterior knurled portions secured to said terminalsspaced from the ends of said sheath and having said knurled portionsembedded in said molded mass of insulating sealing material, the sidesand outer surfaces of said mass 0! insulating material being exposed andthe adherence of said mass to said side of said support, and theportions of said sheath, terminals and terminal members embedded therebyconstituting the sole supporting means for said mass.

CHARLES P. RANDOLPH.

